原理
流程图
301129-a1159ef51f453da8.png
代码实现
进行一次发送消息会在相关的类对象中搜索方法列表，如果找不到则会沿着继承树一直搜索直到继承树的根部(通常为NSObject)，如果还是找不到并且消息转发都失败了就会执行doesNotRecognizeSelector:方法报 unrecongnized selector
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
//执行foo函数
[self performSelector:@selector(test)];
}
+ (BOOL)resolveInstanceMethod:(SEL)sel {
return YES;//返回YES，进入下一步转发
}
- (id)forwardingTargetForSelector:(SEL)aSelector {
return nil;//返回nil，进入下一步转发
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
if ([NSStringFromSelector(aSelector) isEqualToString:@"test"]) {
return [NSMethodSignature signatureWithObjCTypes:"v@:"];
}
return [super methodSignatureForSelector:aSelector];
}
- (void)forwardInvocation:(NSInvocation *)anInvocation {
SEL sel = anInvocation.selector;
Person *p = [Person new];
if([p respondsToSelector:sel]) {
[anInvocation invokeWithTarget:p];
}
else {
[self doesNotRecognizeSelector:sel];
}
}
@end
